The machining of metal--drilling, milling, turning, grinding, and the like--is conventionally carried out with the aid of a metalworking fluid. This fluid is directed as a stream, spray, or mist against the point where the machining is taking place, providing cooling, lubrication, and cleaning of the machine tool and the piece of metal being machined ("the workpiece") while also affording rust and corrosion protection to susceptible metal surfaces. Whereas some machining is still carried out with the aid of oil-based metalworking fluids, the preponderance is done with water-based fluids, of which there are three major types:
soluble oils (emulsifiable oils)--petroleum oils containing emulsifying agents which disperse readily in water, forming milky oil-in-water emulsions; PA1 synthetics (chemical solutions)--concentrated water solutions of lubricating agents, corrosion inhibitors, and other additives; PA1 semisynthetics (microemulsions)--concentrated water solutions of emulsifying agents containing small amounts of highly dispersed petroleum oil. PA1 metal chips, metal fines, and debris from the machining operation; PA1 hydraulic fluids and petroleum-based lubricating oils leaking from the machine and finding their way into the metalworking fluid ("tramp oil"); PA1 dissolved minerals and salts which build up in the metalworking fluid ("total dissolved solids" or "TDS"); PA1 microorganisms (bacteria and fungi). PA1 1) Collecting used and contaminated water-based metalworking fluid in a used fluid storage and settling tank; PA1 2) Allowing the fluid to sit undisturbed in order to allow solid contaminants to settle to the bottom; and/or PA1 3) Passing the used fluid from the storage tank through supplemental filters to remove solid contaminants therefrom; PA1 4) Passing the fluid into a mixing tank and injecting low pressure steam beneath the surface of the liquid in order to create mild agitation within said fluid and to raise its temperature to pasteurization temperature; PA1 5) Skimming or otherwise drawing off separated oil from the top of the pasteurized fluid in the mixing tank; PA1 6) Passing the pasteurized fluid through a heat exchanger to cool it back to ambient temperature; and finally PA1 7) Transferring the fluid to a clean fluid storage tank, thereby obtaining clean recycled fluid suitable for re-use in a machining operation. PA1 1) It raises the temperature of the fluid to pasteurization temperature (160.degree.-200.degree. F.) to destroy bacteria and fungi; PA1 2) It provides gentle mixing to the fluid to keep relatively unstable emulsions and the like from separating; PA1 3) It provides a lifting action to carry droplets of tramp oil to the surface of the fluid for eventual removal; PA1 4) It partially condenses in the fluid as distilled water which lowers the level of total dissolved solids (TDS) and thereby enhances emulsion stability; PA1 5) It helps strip volatile and malodorous impurities created by the action of bacteria and fungi, such as hydrogen sulfide, from the fluid. It is a preferred embodiment of my invention to mount an exhaust fan or other fume removal means at the top of the mixing tank to carry off and capture objectionable fumes.
These fluids are supplied as concentrates which are then diluted with water, usually to from 2 to 10% concentration, before being charged to the machines.
Once in use, metalworking fluids rapidly pick up contaminants as they circulate through the machines. These contaminants gradually build up in the fluid and interfere with fluid performance to the degree that the fluid must eventually be changed out of the machine. The major contaminants are the following:
Of these, bacteria and fungi are by far the most destructive. Common bacteria such as pseudomonas and desulfovibrio and common fungi such as Candida and Fusarium can thrive in water-based metalworking fluids, consuming essential fluid additives and creating slime, sediment, corrosive by-products, and offensive and toxic odors. Traditionally, the most common reason for changing a metalworking fluid out of a machine has been the rancidity caused by bacteria and fungi.